Integrated circuits (ICs) typically generate heat when powered by an electric source such as a power supply. Overheating causes damage to the IC. Increases in clock speed, and device activity and the number of devices increases heating of the IC. A thermal management device employing a thermal sensor is typically used to prevent ICs from overheating. The thermal sensor detects a temperature of the IC. Analog circuitry is used to detect the temperature of the IC, and voltage and current characteristics are changed depending upon the temperature of the IC.
An output of the thermal sensor includes a temperature-independent (fixed reference) signal and a temperature-dependent signal and is input to an analog-to-digital converter (ADC) and transformed from voltage-to-frequency, voltage-to-voltage, current-to-voltage, and current-to-time based on a temperature detected by the thermal sensor. The transformed signals are compared with each other to determine a ratio of the temperature-dependent signal over the temperature-independent signal. A linear transfer of voltage-to-frequency, for example, is a challenge due to sensitivity to process variation. In some existing methods, sigma-delta ADC's are used and are based on sigma-delta modulation (SDM). The sigma-delta ADCs typically include a sigma-delta modulator (i.e., a first-order modulator) and a digital decimation filter. The sigma-delta modulator includes an integrator, a quantizer, a loop filter, and a feedback path including a digital-to-analog converter (DAC) which performs digital-to-analog conversion based on a reference signal Vref. The output of the DAC is subtracted from the input signal at the adder and an output of the quantizer is processed in the digital decimation filter.